DESCRIPTION: The long-range objective of the proposed research is to elucidate the fundamental principles that govern differential and selective messenger RNA (mRNA) degradation in mammalian cells. What cis-acting elements in an mRNA determine its half-life? What regulatory factors and enzymes are involved in degrading mRNAs? How are mRNA stabilities regulated? Towards achieving that goal, this proposal focuses on the molecular mechanisms by which a group of AU-rich elements (AREs) functions to mediate rapid mRNA degradation. AREs are found in the 3' untranslated region of many highly unstable immediate-early-gene mRNAs that code for oncoproteins, nuclear transcription factors and cytokines. They represent the most common RNA stability determinant among those characterized in mammalian cells. Five specific aims are proposed. The first aim is to identify and characterize the key sequence features of AREs and determine their roles in specifying the destabilizing function of AREs. This will involve creating defined mutations of different AREs and testing them by in vivo gene transfection experiments. The second aim is to investigate the role of the 3' poly(A) tail and the nucleolytic events that are indicative of the ARE-mediated decay pathways. The third aim is to identify and characterize the cellular factors that participate in the ARE-mediated mRNA degradation. The fourth aim is to investigate the mechanisms by which differential regulation of the ARE function is achieved. The final aim is to study the relationship between translation and the ARE-directed mRNAdecay. The proposed studies may enhance the knowledge of a fundamental aspect of gene expression that presently is poorly understood. Because the marked instability of several ARE-containing proto-oncogene mRNAs helps to prevent oncogenic transformation by these genes, the regulatory proteins involved in rapid turnover of these proto-oncogene mRNAs may themselves be potential products of cancer suppressor genes. Therefore, the knowledge learned from the proposed research may ultimately be of value to understanding molecular mechanisms of tumorigenesis.